1. Field of the Invention
This invention relates to robotic end-effectors and more particularly to a robotic end-effector with an active system compliance and the ability for micro-positioning.
2. Description of the Related Art
A major component of the Space Shuttle Thermal Protection System (TPS) consists of approximately twenty thousand "ceramic" tiles located on the underside of the vehicle. If these tiles were allowed to absorb water, for example, from the humidity in the air, the water would freeze and the tiles would crack and possibly fall off during flight. To prevent this, each tile is manually injected with dimethylethoxysilane, (DMES) which evaporates during the heat of re-entry. Therefore, the injection process is repeated after every flight.
The present manual injection process is accomplished using a needle-less gun system that was designed and fabricated by Rockwell International Corporation. The technician places a room temperature vulcanizer (RTV) nozzle over a small pin-hole on the tile emittance ceramic coating and injects 2 cc of DMES into the tile. The injection is immediately followed by a 4 second high-pressure gaseous nitrogen (GN2) cycle that disperses the DMES as a gas throughout the internal tile volume. The gaseous form of DMES then reacts and bonds with the silica fibers inside the tile, rendering it waterproofed. On occasion, if an injection is unsuccessful, for example because the hole is plugged, the DMES fluid squirts out between the nozzle and tile rather than entering the tile through the pinhole. Additional technicians record the results of each injection on tile maps. DMES is flammable and hazardous. Technicians are required to wear organic vapor respirators, solvent impermeable gloves, face-shields/goggles, and smocks/coveralls. Because of the high volatility of DMES, the vapors disperse throughout the Orbiter Processing Facility (OPF). Re-waterproofing therefore occurs only during third shift, when few people are present. The entire process is time consuming and the technicians are susceptible to fatigue and errors. It has been very desirable, therefore, to automate the waterproofing of the Space Shuttle thermal protection system.
Several types of robotic end-effectors are known in the art. For example, a patent, search has revealed the following patents:
U.S. Pat. No. 4,955,654, issued to Tsuchihashi et al., discloses an end effector secured to a front end of a manipulator of a remote manipulator system and having a function for clamping dedicated objects, wherein a force applied to the end-effector at the time of clamping the dedicated object is detected so that a driving portion of the end-effector is feedback-controlled in order to protect the end-effector from being applied with a force (or torque) exceeding a predetermined level. The Tsuchihashi et al. device uses force feedback to prevent excessive force when the end-effector clamps a grapple fixture.
U.S. Pat. No. 3,952,880, issued to Hill et al., discloses an end effector, such as a hand, comprising a pair of jaws relatively pivotally movable between open and closed positions under operation of power means such as an electric motor. Sensing means, for sensing both magnitude and direction of forces along three mutually orthogonal axes intersecting at the wrist end for sensing magnitude and direction of torques about the axes, are provided at the wrist intermediate to the manipulator hand and hand supporting means. The sensing means includes a plurality of sensing units radially spaced from the longitudinal axis of the manipulator at equal distances therefrom.
Both Tsuchihashi et al. and Hill et al. references use force feedback to monitor the applied force. However, these devices do not de-couple the forces created by the manipulator from the object they are handling.
U.S. Pat. No. 5,172,922, issued to Kowaleski et al. and U.S. Pat. No. 4,945,979, issued to Cullen et al. disclose end effectors which utilize springs for self-aligning.
All of the aforementioned patents are required to be positioned by a manipulator arm. They lack the ability to self-position.